All You Need to Know About Genetic Testing for Patients Treated With Fluorouracil and Capecitabine: A Practitioner-Friendly Guide.

Fluoropyrimidines (fluorouracil, capecitabine, and other analogs) are highly used anticancer drugs worldwide. However, patients with cancer treated with these drugs might experience severe, life-threatening toxicity because of germline genetic variation in the gene. This is a genetic predisposition with an established mechanistic basis that links genetic variation in the gene to an increase in systemic drug exposure, resulting in an increased risk of toxicity. Pharmacology guidelines provide recommendations on avoiding treatment with fluoropyrimidines or reducing their dose in patients carrying genetic variants conferring an increased risk of toxicity. However, oncology societies in the United States do not recommend systematic testing. Instead, on April 30, 2020, the European Society for Medical Oncology issued a document recommending genetic testing. In this scenario of contradicting information, practicing oncologists struggle with reaching an informed decision on whether genetic testing should be applied before treatment. This is mostly due to uncertainty about the clinical relevance of genetic testing from the perspective of a practicing oncologist. To reach an informed decision, practicing oncologists need access to concise information on the genetic variants to be tested and a practitioner-friendly interpretation of the test results. We believe this information is currently lacking. To our knowledge, for the first time, we provide a single guide for health care professionals to make an evidence-based decision about testing for patients with cancer. This article provides the essential knowledge base for oncologists to have an informed discussion with their patients about the genetic testing for . This document assists practitioners in quickly evaluating whether, when, where, and how to order a genetic test.